Robot capabilities range from very simple repetitive point to point motions to extremely versatile movement that can be controlled in sequence by a computer as a part of a complete integrated manufacturing system. Robots have been used in many material processing applications including cutting, trimming and welding.
Laser applications can be divided into several general categories including the measurement of spatial parameters, material heating and/or removal, non-destructive probing of resonant phenomena, communications, optical processing, laser-induced chemical reactions and wepons.
The combination of a laser with a robot allows the laser to operate with a degree of freedom previously unknown. The combination of the two technologies, if successfully performed, is suitable for most laser applications, including material processing applications. The same laser can be used in processing many kinds of materials by controlling the speed and the power of the laser. The laser can cut metal, cut glass, trim plastic or weld aluminum. Because robots are typically controlled by a programmed computer, the same computer can be used to regulate the laser's power. Consequently, in a flexible manufacturing line, parts can be cut or welded one after the other simply by adjusting the power of the laser.
Lasers are currently in operation in both commerical and industrial environments. For example, many parts of an automobile are processed with lasers. Also, a large percentage of vision systems that measure depth are laser-based.
Another industrial use of the laser is laser-assisted machining wherein the laser beam is applied in front of a cutting tool to reduce tool wear and cutting forces. Such an application results in fewer tool changes, decreased total tool wear and tool cost, increased cutting speeds and increased amounts of materials that can be cut.
Two types of lasers are typically used in material processing applications, solid state and carbon dioxide lasers. The carbon dioxide lasers are relatively unlimited in power. The solid state lasers are limited in power and require more elaborate shielding than the carbon dioxide lasers.
Popular uses for metal-working lasers include seam, spot and fusion welding, cutting, drilling, surface hardening, metal marking, scarfing, deburring, trimming and heat treating. The advantages of laser processing are particularly evident in welding. Welding done with lasers often requires no additional work such as grinding. With traditional welding, welds must be reworked a large percentage of the time. Therefore, cost savings are an important aspect of laser welding.
Two methods have developed in order to link lasers with robots. One method is to move a part via a robot into the laser beam. The other way is to move the beam via the robot to the part. The latter method is effective if the part is too large to be moved easily or when contouring is necessary.
One method of moving the beam via the robot to the part incorporates two mirrors in each jount (i.e. optical joint) of a tubular linkage mechanism which is manipulated by the robot to direct the laser beam along the desired path. It has proven difficult to hold the mirrors in place very securely and precisely enough for the beam cannot be misdirected even a fraction of a degree as it proceeds along its path. Dynamics of the robot usually affect the mirror positions and must be taken into account in such a design.
A focusing lens positioned in such a mechanism concentrates the laser energy and directs it to a singular point with a high power density. Consequently, the robot must be very accurate to direct the beam to a precise area on a workpiece. A longer focal length lens can be used to compensate for robot inaccuracies. However, the resulting beam is focused over a larger area so that both power density and speed are lower.
Despite the above-noted problems in linking the laser with the robot, it is highly desirable to forge this linkage especially because the laser is an ever sharp tool having a non-contact method of operation. The use of the laser also eliminates tactile feedback and tool wear because the laser and the part do not touch each other.
Elimination of even one robot mirror from the total number of mirrors in a laser robot system is important for the following reasons: (1) significant cost savings can be realized due to the relatively high cost of the mirrors compared to other components of the system; (2) the efficiency of power transmission is increased since power losses of the collimated laser beam are almost entirely attributed to the absorption of energy which occurs at each mirror; (3) initial alignment of the beam delivery system is simplified with fewer mirrors to align, thereby minimizing the magnitude of the resultant alignment error which is practically achievable; and (4) system reliability is increased and a reduction in required maintenance is achieved with fewer mirrors to clean and maintain in alignment.
The U.S. Pat. No. to Plankenhorn 4,539,642 discloses a method of linking a robot with a laser including a laser arm which is manipulated by the robot. The laser arm is supported by the robot arm and is aligned to move in synchronization with the robot joints. The laser arm must be mounted to the robot arm in a precision synchronized fashion.
The U.S. Pat. No. to Akeel 4,650,952 discloses a robot laser system wherein the robot has a number of degrees of freedom constituted by two orthogonally related linear movements along intersecting longitudinal axes and two orthogonally related rotary joints having intersecting pivotal axes.
The U.S. Pat. No. to Nakashima et al 4,706,001 discloses an industrial robot having pressurized, airtight chambers in which electric motors are housed.
The U.S. Pat. No. to Monteith et al 4,695,701 discloses a laser robot system including a laser wrist.
The U.S. Pat. No. to Bisiach 4,677,274 discloses a robot laser system wherein the laser beam reaches the robot through a side opening therein whereafter it is axially directed by a pair of adjustable mirrors to a hollow head. Neither of these mirrors is mounted at the intersection of two pivotal axes.
The U.S. Pat. No. to Marinoni 4,698,483 discloses a robot laser system wherein the robot includes a base and a fork element supported vertically and rotatably by the base. An arm is articulated at its first end to the fork element about a substantially horizontal axis. A forearm is articulated to a second end of the arm about a substantially horizontal axis. A wrist assembly is mounted at the unarticulated end of the forearm, is rotatable about an axis parallel to the forearm and has an end portion which supports a lens for focusing the laser beam, unlike the above-noted Plankenhorn patent which discloses a laser beam path fully contained in a structure coupled to move in synchronism with the main robot structure. The Marinoni patent utilizes the robot structure for passage of the laser beam for segments of its laser path.
The U.S. Pat. No. to Rando et al 4,698,479 discloses the use of sealed, sliding telescoping tubes in a laser beam delivery system.
Japanese Patent Document Ser. No. 59-107785 discloses a laser robot system including a robot having a motorized multi-joint arm provided with reflecting mirrors at the ends of the arm parts.
Japanese Patent Document No. 59-223188 discloses a laser beam machine having a reflecting mirror provided in each joint portion of a manipulator.